Ring detectors of the prior art generally employ a d.c. blocking capacitor in series with a relay and rectifier across the telephone line that are switched out of circuit after ring up. In a later device, the telephone line is loosely inductively coupled to a transistor that amplifies pulses produced at the start and stop of each ring burst. Another circuit couples the line through a rectifier and capacitor charging circuit to a normally on transistor to cause the transistor to cease conduction when a ring signal appears. In another device, a separate ringing line many miles long is directly connected to a transistor that amplifies a ringing voltage attenuated by the distance.
In this invention, a capacity coupled high impedance ring detector operates on low ringing power to provide a useful means for actuating equipment when a ring signal appears, with a simple semiconductor circuit that may replace relatively large and costly relays, reducing costs and conserving space.
It is another object of this invention to detect ringing voltage and by light loading of the line and lack of d.c. flow, not to interfere with telephone service, to cause low attenuation of voice signals and that need not be switched out of the telephone line after ringing is tripped and line seizure is established.